Factions in a strategy game

I haven’t played starcraft in years, and when I did it was minimal. A few months ago, Namaste got back into playing it. I remember walking in his room to see Terran soldiers firing their machine guns, running on top of purple slime from which spikes were emerging and killing them. Later I learned that the purple slime just designates the area where Zerg can build, and the spikes were just a defensive building. However, the image had a strong effect on me.

I want to see a strategy game with (at least) three factions which are fundamentally different. Namaste put it well: “one side has units, another side doesn’t have units”. For example, you’d have the typical RTS faction with buildings that produce units that have guns. But another faction could be plants that only have biological weapons; they couldn’t chop anybody’s head off, but they could cause disease, metal corrosion, suffication, etc. Plants of course cannot move, but can spread their seeds. Perhaps a third faction would be a small tribe of people who could control animals, or something like that.

UPDATE: Namaste and I talked about it a bit. An interesting idea is a faction who only have “energy concentration” in areas, and that energy could take whatever form it likes. That is, you could have an oversized watch tower that could convert into an army when it needed to.